Nodular cast iron and process of manufacture thereof



NonULAR CAST IRON AND PRoCEss'oF MANUFAQTURE THEREOF Filed Nov. 2s, 1955 T. W. CURRY Jan. 6, 1959 2 Sheets-Sheet 1 kaQhhN la SvN moms w. aun/w FILES 595e "mustn .NNN lmkm.

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United States Patent O NODULAR CAST IRON AND PROCESS OF MANUFACTURE THEREOF Thomas Wetzel Curry, Lynchburg, Va.

Application November 28, 1955, Serial No. 549,322

16 Claims. (Cl. 148-3) My invention relates to an improved method of making nodular, or so-called ductile iron.

Nodular iron made by known processes was sometimes of a grade which could not be used commercially because of deficiencies in the controls. Where the controls used in the manufacture of nodular iron were such as to give good results, the expense of the control methods made the operations commercially unsatisfactory considering many of the commercially available starting materials and additives.

It is to disclose a process where all the controls can be delicately and accurately employed in such a way as to give universally good results, and where the expense of the combination of steps is such as to be economically competitive with related ferrous and nonferro-us compositions, that I have devised this process.

Other objects and advantages will appear from the ensuing description.

In the drawings:

Figure 1 is a flow sheet of my process.

Figure 2 is a photomicrograph of the metal in a regular super de Lavaud pipe.

Figure 3 is a photomicrograph of the metal in a pipe made by my process.

Figure 4 is a photomicrograph of the metal in an etched specimen from regular super deLavaud pipe.

Figure 5 is a photomicrograph of the metal in an etched specimen from pipe made by my process.

Though I am describing this process as applied to pipe, it also applies to other types of chilled castings. Since the nodular (ductile) iron pipe is very desirable i'n the pipe industry, the following description deals primarily with the manufacture of such pipe. The process is particularly applicable to chilled casting such as may be produced by the de Lavaud process Where pipe is centrifugally cast in steel molds and the pipe is then annealed.

Wall thickness in nodular iron pipe can be made thinner and yet have the same or greater strength as gray iron pipe of greater wall thickness. Moreover, the ductility of such nodular pipe is considerably higher than such gray iron pipe and it is less subject to rupture through shock. It is noteworthy that my process has particular application, as before stated, to cast products for instance such as are made by the de Lavaud centrifugal casting process, because in such processes the molten iron is cast against a chill mold and must be annealed thereafter.

The following, for example, is a comparison of the mechanical properties of pipe made by the de Lavaud steel mold casting process where gray iron pipe is produced and a nodular iron pipe of the salme diameter and less wall thickness as made by my process and similarly cast in a de Lavaud centrifugal steel mold. Both of these pipes have been annealed after casting.

ice

DE LAVAUD PROCESS Conventional Gray Iron 8 Diameter Pipe Present Nodular Iron 18,000-29,000 Bursting Tensile 46,000-53,000

Strength, p. s. i.1

40,000-60,000 Modulus of Rnp- 100,000-120,000.

ture (Ring), p. s. i.

40,000-60,000 Modulus of Rup- 100,000-115,000.

ture (Strip), p. s. 1.

9,000,000-12,000,000 Modulus 0f Elastic- 3,100,000-5,500,000.

ity (Ring), p. s. i. Modulus of Elasticity (Strip), p. s. i. Ultimate Tensile 1" keel-455,000-

Ordinarily, if the ductility and ultimate strength of a metal is increasing, the modulus of elasticity will increase. In testing all mechanical properties of pipe, as above, the Cast Iron Pipe Association uses the secant of the modulus of elasticity and therefore the lower the ME, the better the mechanical properties of the pipe.

It is appar-ent from the above chart that the design of the present nodular iron pipe with. its better mechanical properties could be modified, particularly its wall thickness, and 'thus perform much more satisfactorily than conventional gray iron pipe. This reduction in the wall thickness of the pipe would also result in savings in costs.

Prior tests with nodular iron in the de Lavaud process made with processes other than that described herein have presented a casting problem in that the inside and outside surfaces of the pipe werel rough and unserviceable. Such pipe had adhering non-metallic inclusions. Moreover, in these prior art processes the 'fluidity of the metal was such that best results were obtained by increasing the wall thickness beyond that required for the standard gray iron pipe. It was also found that nodular iron made by still other processesl investigated required a higher pouring temperature at the expense of steel mold life, to produce a usable but not commercially satisfactory surface on the inside and outside of the pipe.

In order to make good nodular iron, for instance, such as can be used in pipe with advantage, it is quite necessary to have flexible controls throughout the proc-y ess. For instance, some of the constituents which must be controlled within desirable limits arel percentages of carbon, sulphur, manganese, silicon and phosphorus. In general, the ferrous materials included within the cupola charge comprise cast iron and steel scrap and returns from the nodular pipe casting process. Asa practical matter, it is desirable when charging steel scrap to eliminate from the scrap, before melting, armatures of electric motors beca-.use of the presenceA yof copper, to eliminate rubber covered steel because of high sulphur content and also to eliminate aluminum and bearing metals.

Steel scrap containing these inhibiting elements ad* versely affects the desired formation of spheroidalgraph-y ite. Always a Very small percent o-f these inhibiting elements in the presence of copper and titanium will upset the process and spoil the product. Due to varia-tions in the chemistry of the ferrous charging materials, control treatments at various stages of the process must be undertaken to bring percentages of the desired constituents and `other elements within a preferred range. These control treatments will be detailed hereinafter.

In general my process comprises a melting stage in which the charging materials are melted, followed by a desulphurization. Sometimes in .practice the desulphurization step may be omitted for often available materials 'and chemical control in melting bring the sulphur content below the desirable maximum. In practice this desulphurization step is normally followed by a re-heating step in which carbon and silicon are adjusted. Of course this third step may be eliminated dependent upon charge and cupola construction. The ensuing `step is a treatment step to treat the molten material with nodularizing agents. Following this treatment step is la step of inoculation to make l'inal adjustment of the elements present in the molten mass. From this inoculation step, the materials pass to a chill casting step which is followed by annealing. v

Referring to the drawings in Figure 1 I have diagrammatically shown a preferred process for carrying 4out my invention. Alternative processes will be apparent from the following description.

Step I In `a typical example, there is charged into a basic cupola in the melting step, No. I, steel scrap and cast iron suchl as returns from the nodular cast pipe together with coke and limestone to form Ia basic flux. All this material is charged into the cupola and air is blown in to obtain a molten material, the range of temperature being 2850-2950 F.

This molten metal is run into a forehearth, or ladle, in the second step for desulphurization. A cooling of molten mass occurs and it leaves Ithe forehearth, or ladle, at about 2500-2600 F.

` A typical charge in the cupola of Step I is as follows:

'I'he sulphur content of the metal tapped from the lcupola may be in the range of from 0.1 to 0.5%. Under normal operating conditions, it is expected that the sulphur content of this metal will not exceed 0.02% maximum. Where the sulphur content of the metal from the `cupola is in excess of 0.02%, then desulphurization, Step II, is utilized. Of course, metal with a sulphur content less than 0.02% will normally proceed directly from thc 4cupola to the electric furnace since Step I-I desulphurization is unnecessary. The sulphur content here, carrying over through Step III, is essential for the successful functioning -of subsequent Step IV. As stated, the molten metal as taken from the cupola (Step I) is at a temperature of from 2850-2950 F.; but heat loss in transfer and desulphurization (Step II) lowers the temperature of the molten metal to 2500-2600 F,

Siep 111 IStep II-I in the diagrammatic drawings shows `an electric furnace where the molten mass is reheated to raise its temperature, and percentages of carbon and silicon are adjusted, as is shown below. The metal charged into the basic electric furnace in Step III has steel scrap and 50% ferro-silicon added to adjust the carbon and silicon contents. The temperature of the metal after de- Y sulp'hurization -is in the range of 250G-2600 F.; after Composition of Metal Basic Cupola Metal Charge Si S I Mn P I TC (a) Metal:

; 350# d. i. pipe return Scrap 2. 0. 02 0. 45 0. 10 3. 50 1650# steel scrap 0. 20 0. 05 0. 50 O. 05 0. 20 Into Basic cupola charge 0. 0. 045 0. 49 O. 059 0. 78 Out of cupola spout 2,850-

2,950 F l 0. 40 0. 05 0. 45 0. 10 0 (b) Coke and tlux per ton of 50 p metal charged into basic cupola:

150# Stone 350# Coke 1 Silicon loss in cupola is calculated at 33%. 5 5

The percentages of steel scrap and nodular iron returns shown in the cupola charge may be varied depending upon shop circumstances. Steel scrap would be in the range of 50% to 100% of the charge with nodular iron pipe returns scrap or cast scrap, making up the balance. The silicon content of the metal out lot' the cupola would be in the range of from 0.30% to 1.40%,

Step Il Calcium Carbide Injection per Ton Si S Mn P TG 10# Calcium Carbide 7 cubic feet nitrogen Analysis 0.40 0. 02 0. 45 0.10 4. 20

these Step III additions have been made it is raised to 2850-2900 F.y p

Thefollowing is typical of the operating conditions of Step III:

'METAL CHARGE TO ELECTRIC FURNACE 1825# cupola metal 175# special steel scrap (ccld) g# 1501?, FeSi (calculated at 48% Si content and 10% 1 oss 090# Si S Mn P TC Into Electric Furnace 2. 43 0.023 0.45 0.10 3.69 Out of Electric Furnace 1 2.19 0.023 0.45 0.10 2 3. 50

1 Silicon loss in electric furnace calculated at 10%. 2 Carbon loss in electric furnace calculated at 5%.

- silicon alloy addition but the process will work equally well if any commercial grade of -ferro-silicon would be substituted for the 50% grade. 50% ferro-silicon means 50% rsilicon in the iron alloy. Commercial grades that can be used are the commercial grades that run 30% silicon in a ferrous alloy, to 90% silicon in a ferrous alloy.

Step IV In the next step, Step IV, the metal is passed to a treatment or 4transfer ladle in which nodularizing materials are injected. The metal is tapped from the electric furnace of Step III in amounts suitable for handling in the de Lavaud pipe Shop. As each tap of metal is made, an injection of calcium carbide and the nodulariz'ing agent is made in the transfer ladle from the electric furnace to the pipe shop. The treatment of the molten iron at 2850-2900 F. as it enters the nodularizing treatment ladle, Step IV, gives an iron that will form graphitic nodules when annealed (Step VII) if inoculation (Step V) in provided as it is poured into the pipe machine ladle (Step III) as hereinafter explained. The molten mass leaves this nodularizing treatment ladle at about 2 650" F,

(a) INJECTION OF NODULARIZING ALLOY AND CAL- CIUM CARBIDE PER TON 6.4# alloyed mixture of Mg, Ce, Si 14.4# calcium carbide 10 cubic feet nitrogen carrier gas Si S Mn P TC Analysis 2. 39 0. 015 0. 45 0. l0 3. 50

The silicon content in Step IV shown in the example can be in the range of 2.00% to 2.45% and the total carbon content could be in the range of 3.40% to 3.70%, and the process would be satisfactory.

The nodularizing alloy used simultaneously with the calcium carbide can be a magnesium-cerium-silicon ferro alloy. A typical injection as indicated in the figures given above comprises a simultaneous injection of 14.4 lb./T. calcium carbide and 6.4 lb./T. of magnesiumcerium-silicon ferro alloy in l cu. ft. of nitrogen carrier gas. It will be appreciated that in recovering such critical quantities of residual magnesium in the metal, under these conditions, a control against magnesium oxidation must be elected during injection. For this reason, I have selected the above ratio of carbide to magnesium and great care is taken to inject the alloy and carbide at precisely the same moment.

In this nodularization we recover from between .005% to .009% magnesium in the annealed product. Otherwise stated, there is a 25% recovery of residual magnesium considering the amount of magnesium alloy added. Residual magnesium in excess of .01% does not produce the structure desired in the pipe with the annealing cycle employed in the process. Residual magnesium from .0054.009 will give the desired properties.

In the present process the preferred nodularizing magnesium alloy is an iron-silicon-cerium alloy.

Many magnesium-cerium-silicon ferro alloys are susceptible of satisfactory employment in my process. Economics, of course, will be affected with major changes in the cerium and magnesium contents of these nodularizing alloys. In general, alloys, the composition of which will fall within the limits expressed below in percentages by weight, may be used:

Percent Percent Percent Percent Percent Ce Si A`g Ca p After the metal has been treated by the injection of the calcium carbide and the nodularizing agent in the nodularizing treatment ladle, it is transferred to the de Lavaud pipe machine floor. Generally, the metal is held less than ten minutes in the nodularizing treatment ladle.

Step V Ferro-Silicon Addition Ccmpostion of Metal vat deLavaud Machine Ladle-# 757 grade ferrfsilicon ansy ffr ladle addr si s Mn P To tion Analysis 2. 54 i o. 015 o. 45 0.10 3. 5o

This nal addition of grade ferro-silicon alloy (75% silicon) can be changed to any commercial grade or even pure silicon metal; the actual silicon addition may vary from 0.15% to 0.60% of the total molten mass. It is to be noted, however, that the addition of this silicon (Step V) over that added during nodularization (Step IV) is 0.15%.

The final molten iron is now ready to pass into the de Lavaud machine for casting and has a temperature of 2400-2550 F.

Step Vl In Step VI, the pipes are cast in the de Lavaud machine.

Step VII In Step VII, the cast pipe are charged into the annealing oven and annealed. The annealing performs two major functions: (l) to transform massive carbide and (2) to transform the pearlite that forms when the iron cools through the temperature range (1350l250 F.). The annealed product is a nodular iron pipe.

Since this isa process in which metallurgical control features are of paramount importance, I will now describe in detail the controls used.

CARBON CONTROL The total carbon content of the metal as it is tapped from the electric furnace for conversion to nodular iron can be controlled within a close range in a number of ways. With a slag of a basic composition, the total carbon content of the metal tapped from the cupola will be in the range of 4.0 to 4.2% and can be adjusted downward to the desired level by an addition of cold steel scrap in the electric furnace. There are possiblities to reduce the carbon content of the metal as tapped from the basic cupola, by changing the composition of the basic slag and thereby reducing the amount of cold steel scrap to be added in the electric furnace. If, in the process of refining the basic slag for the most economical electric furnace operation, the total carbon content is lowered below the desired level, carbon could be added to the bath by the injection process.

CONTROL OF MANGANESE The manganese control of our raw materials is somewhat xed so that the melt from the basic cupola will contain manganese in the range of 0.35% to 0.55%. A nodular iron containing manganese in this range will anneal satisfactorily in our annealing oven. There is a possibility, however, of some manganese steel scrap or other scrap materials containing manganese higher than the indicated desired level, entering into the cupola mixture. The manganese content, in these few instances, may be adjusted to the desired level by an addition in in Step III in the electric furnace of converter metal which would be on hand to take care of this adjustment, or the use of a special low-manganese pig iron purchased from an outside source.

The converter metal referred to is one low in manganese, silicon and carbon. The use of the converter metal takes the manganese percentage down and silicon and carbon can be added if necessary to obtain the desired percentage of these elements.

CONTROL OF SILICON It is to be expected in this process, that the silicon content of the metal in the electric furnace would always be on the low side of the desired range. Silicon can be added in the electric furnace by an addition of any of the commercial grades of ferro-silicon, or by the injection of silicon metal.

In the extreme case of having the silicon content too high, pig converter metal or steel scrap could be added. These materials would, in lowering the silicon content,

lower the carbon content and carbon may be injected to raise vthe level to the desired range.

CONTROL OF PHOSPHORUS The phosphorus content of the nodular iron pipe should not exceed 0.12% for best physical properties. If, in the use of high percentages of cast scrap in the cupola charge, the phosphorus content is above the desired level, steel scrap may be added to the electric furnace to adjust the phosphorus content to 0.12% maximum. The steel scrap addition will lower the total carbon content and the carbon can be adjusted by injection.

In connection with the process and product made by this process, a comparison between regular super de Lavaud pipe contrifugally cast in steel molds and the .thin wallV pipe made by my process described in this application is desirable. The regular super de Lavaud pipe is one with a dense close grain metal which is very suitable for ordinary applications but the tests that follow ywill show that it is in practically every way inferior to the product made by my process. A comparison between the pipes from the point of viewof photomicrographs will indiate radical differences in the structure of the metal. Pipe made by my process has physical propernURs'rrNGv TESTS Y [Tests made on 15-7}2' lengths of plain end pipe. Pipe burst by applying hydrostatic pressure at a slow steady rate] SUMMARY OF PHYSICAL PROPERTIES Actual Results Requirements Regular New Super Process deLavaud r Strip M/EL 58, 300 107,100 Strip M/E 9, 400, 000 5,020,000 Ring M/R 64, 300 135, 300 Bursting Tensile 29, 900 6B, 500

ties which are ample to justify the thin wall thickness I may employ, for I can have a considerably thinner wall pipe with greater strength than with the regular super de Lavaud pipe.

CHEMICAL COMPOSITION Regular New 6'.' Pipe super Process deLavaud Lab. N0 159, 767 161, 496 Percent Si 1. 78 2. 59 Percent S 0. 055 0.018 Percent Mn 0. 52 0. 54 Percent P 0. 38 0. 10 'Percent TC 3. 74 3. 53 Percent Mg O. 006

PHYSICAL PROPERTIES [Talbot strip tests] Regular New 6" Pipe super Process deLavaud Lbs. Load 635 670 Deection- 130 790 Thickness- 435 250 R 48, 300 107, 100 -M/E 9, 400, 000 5, 020, 000 B-Rockwell 84-81-73 87-87-77 1. Lbs. Load is actual load required to break a 1/2 wide x 12 long strip machined from wall of pipe.

2. Deection is distance strip bent before breaking.

3. Thickness is actual thickness of pipe wall.

4. M/R is Modulus of Rupture which is a measure of strength. Pipe speciiications require that this be in excess of 40,000.

M/E is Modulus of Elasticity which is in this test a measure of stitness or resistance to bending. Pipe specifications require that this not exceed 12,000,000.

6. B-Rockwell is measure of hardness across pipe wall. Pipe specifi lcations require that this not exceed 95.

RING CRUSHING TESTS [Tests made on 3 length rings by standard procedure] Referring to the drawings, Figure 2 is a photomicrograph of the metallic structure in a regular super de Lavaud pipe 6 inches in diameter cast to 0.3 8 inch wall thickness and magnification diameters. The metal here is unetched.

This photomicrograph, Figure 2, shows typical size, pattern and distribution of graphite found in the wall of a regular super de Lavaud pipe. The akes of graphite are numerous and extremely small and are arranged in what is known as a dendritic pattern.

Referring to the drawings, Figure 3 is a photomicrograph of the metallic structure of an iron pipe made by my process. The pipe is 6 inches in diameter with a Wall thickness of 0.25 inch. Here also the magnification is 100 diameters and the metallic surface is unetched.

The graphite particles throughout the wall of the new process pipe are larger and far less numerous than in Figure 2 and generally tend to be somewhat spherical in shape. 'Ihey are quite uniform in distribution and show no tendency to the dendritic pattern shown in photomicrograph Figure 2.

Referring to Figure 4 I have shown a photomicrograph of the metallic structure of a regular super de Lavaud pipe of 6 inches diameter cast to 0.38 inch wall thickness; magnification is 500 diameters and the pipe has been etched with a 2% solution of nitric acid and alcohol.

This photomicrograph is a portion of the field shown in photomicrograph Figure 2 after etching and a higher magnification. The structure consists of a fine graphite network in a matrix of ferrite. A small amount of iron phosphide is visible in the lower portion of the field.

In comparison see Figure 5 which is a photomicrograph of a 6 inch diameter iron pipe made by my process cast to 0.25 inches wall thickness. The surface of the metal has been etched in the customary manner and the magniiication is 500 diameters.

This is a portion of the eld shown in photomicrograph Figure 3 after etching and at a higher magnication. The structure consists of compact particles of graphite in a matrix of practically all ferrite. Traces of pearlite and cementite are present.

MODIFICATION PROCESS An alternate method in the development of the present nodular iron product resides in the use of an acid cupola. In this method the cupola charge naturally varies substantially from that used in the basic cupola as defined hereinbefore. Whereas, the iron melted in the basic cupola method had a high carbon and low sulphur content, in the present alternative method, the ironmelted in the acid cupola has a low carbon and high sulphur content. In this process it is proposed to eliminate reheatsaid elements being tapped from the cupola.

Composition of metal Acid cupola metal charge Per- Per- Per- Per- Percent cent cent cent cent Si S Mn P TC (a) Metal:

500# Steel Scrap 0.20 0.05 0. 50 0. 05 0.20 1430#Basic Cupola Pig Iron. 0.50 0.02 0. 50 0.08 4.20 20 77# Lump, 50% Fe Silicon, 48.0 Into acid cupola charge 2.28 c. 0. 50 3.03 Out of acid cupola 2.00 0 10 0.45 0.10 3.45 (b) Coke and flux per ton of metal charged into acid cupola:

300# Coke 50# Silica rock Dolomtc.-

Sulphur in the iron tapped from the acid cupola would be reducedin desulphurization Step II from 0.10 to 0.02% by an injection of 20# of calcium carbide per ton of metal. In acid melting practice there is a gain in sulphur, phosphorus, total carbon being as shown in the chart. Through this process I usually obtain the following percentages of elements in metal tapped from the acid cupola: 2% silicon; 0.45% manganese; 3A0-3.50% total carbon; 0.10% phosphorus; 0.07 to 0.11% sulphur.

It will be apparent from the foregoing that my processes have produced a valuable iron at reasonable cost with control factors which permit of uniform results in the nal product.

I desire that my invention be limited solely by the sco-pe of the appended claims and the showing of the prior art.

I claim:

1. In the manufacture of chilled cast and annealed nodular iron having spheroidal graphite, graphitic aggregates and flakes, the process of simultaneously injecting molten metal with calcium carbide and a nodulizing alloy containing magnesium, the relative quantity of calcium carbide being sufficient to protect the magnesium from oxidation and to control the amount of residual magnesium within the range of less than 0.01%, then cooling and solidifying the iron and thereafter annealing the casting thereof.

2. The process according to claim l in which the relative quantity of calcium carbide to the nodulizing alloy is in the ratio of approximately 2.25 to l.

3. In the manufacture of chilled cast and annealed nodular iron having spheroidal graphite, graphitic aggregates and Hakes, the process of simultaneously injecting molten metal with calcium carbide and a nodulizing magnesium-cerium-silicon-ferro alloy, the relative quantity of calcium carbide to the nodulizing alloy being sufficient to protect the magnesium from oxidation and to control the amount of residual magnesium in the iron product within the range of less than 0.01%, then cooling and solidifying the iron and thereafter annealing the casting thereof.

4. The process according to claim 3 in which the relative quantity of calcium carbide to the nodulizing alloy is in the ratio of approximately 2.25 to l.

5. In the manufacture of chilled cast and annealed i nodular iron wherein the recovery of 0.005 to 0.009%

residual magnesium in the annealed product is desired, the process of simultaneously injecting calcium carbide and a magnesium-cerium-silicon-ferro alloy in the pres- "5 ence of an inert carrier gas into va molten mass of iron, the relative quantity of calcium carbide being suicient to prevent oxidation of the magnesium .and to control the amount of residual, magnesium in the iron-product then cooling and solidi-fying the iron and thereafter annealing the casting thereof.

6. A process for manufacturing chilled cast and annealed nodular iron having spheroidal graphite, graphitic aggregates and flakes, comprising the steps of: melting iron having a sulfur content no greater than 0.02%, in a basic cupola, sequentially adjusting carbon and silicon content of the melt while reheating same, thereafter injecting the desulfurized melt with calcium carbide and a nodularizing agent containing magnesium simultaneously the relative quantity of calcium carbide to magnesium being suflicient to protect the magnesium from oxidation and to control the amount of residual magnesium within the range of lless than 0.01%, next inoculating the melt with ferro-silicon alloy, thereafter casting the iron on a chill to yield a white iron and finally 'annealing to yield the nodular iron product.

7. A process for manufacturing chilled cast and annealed nodular iron having spheroidal graphite, graphitic aggregates and flakes, comprising the steps of: melting iron having a sulfur content in excess of 0.02% in an acid cupola, sequentially desulfurizing the melt to a percentage of no greater than 0.02%, thereafter injecting the iron melt with calcium carbide and a nodularizing agent containing magnesium simultaneously the relative quantity of calcium carbide to magnesium being suiiicient to protect the magnesium from oxidation and to control the amount of residual magnesium within the range of less than 0.01%, then casting the iron on a chill, and finally annealing to transform the iron to the nodular iron product.

8. A process for the manufacture of chilled cast and annealed nodular iron comprising the steps of: melting an iron charge, desulfurizing the iron by calcium carbide injection to Within the range of 0.02% sulfur, thereafter simultaneously injecting the desulfurized molten iron with calcium carbide and a nodulizing magnesium-ceriumsilicon-ferro alloy wherein the ratio of calcium to magnesium is suicient to prevent oxidation of the magnesium and to control the desired recovery of residual within the range of less than 0.01%, casting the iron which is white in the as-cast form and sequentially annealing same to yield the nodular iron.

9. The process according to claim 8 including the step of adjusting carbon and silicon -contents of the metal following desulfurization by adding steel scrap and at least one ferro-silicon alloy and raising the temperature of the iron before injecting with the mixture of calcium carbide and the nodularizing alloy.

10. The process of claim 9 in which commercial grade ferro-silicon alloy is used with steel scrap in adjusting carbon and silicon contents of the iron.

11. The process of claim 9 in which a standard grade of pig iron is used with steel scrap in adjusting carbon and silicon contents of the iron.

12. A process for the manufacture of chilled cast and annealed nodular iron comprising the steps of z charging a cupola with steel scrap, cast iron, pig iron, coke and flux, and heating to 2850-2950 F. to form a melt, sequentially desulfurizing the iron melt by calcium carbide injection, passing the desulfurized melt to a step where carbon and silicon contents are adjusted and iron reheated to a temperature of 2850-2900 F., immediately thereafter injecting the desulfurized iron with calcium carbide and a nodularizing magnesium-cerium-siliconferro alloy simultaneously, wherein the ratio of calcium carbide to magnesium is suiiicient to prevent oxidation of the magnesium and to control the desired quantitative recovery of residual magnesium, casting the iron against a chill and sequentially annealing the white cast iron. 13. The process of claim 12 including inoculating the iron with a ferro-silicon alloy following treatment with the magnesium nodularizing alloy and immediately preceding chill casting.

14. The process according to claim 13 in which calcium carbide is injected in the desulfurization of the iron melt with nitrogen as a carrier and in which the calcium carbide and nodularizing agent magnesium-cerium-silicon-ferro alloy are added simultaneously as a mixture with an inert gas as a carrier.

15. A process for manufacturing chilled cast and annealed nodular iron comprising the steps of: heating a charge of steel scrap, cast iron scrap, and pig iron in a cupola to 2850-2950 F., desulfurizing the melt in a ladle by injecting calcium carbide with a nitrogen gas carrier, skimming the slag, raising the temperature of the melt to 2850-2900" F., and adjusting the carbon and silicon contents by ferro-silicon and steel scrap additions,

next passing the melt to a step where a nodularizing agent comprising a rnagnesium-cerium-silicon-ferro alloy is added with an inert gas as a carrier and calcium carbide as a deoxidzer and desulfurizer, passing the melt at about 2650 vF. to a ladle where there is a nal ferro-silicon inoculation to raise the silicon content of the molten mass immediately preceding casting, then passing the molten mass to casting and thereafter annealing the casting.

16. A process for the manufacture of chilled cast and annealed nodular iron, comprising the steps of: melting an iron charge, desulfurizing the iron by calcium carbide injection, thereafter adjusting the carbon and silicon con? tent of the iron by adding steel scrap anda ferro-silicon alloy and raising the temperature of the iron, next simultaneously injecting the de-sulfurized iron with the mixture of calcium carbide and a nodularizing magnesium-ceriumsilicon-ferro alloy wherein the ratio of calcium carbide to magnesium is suii'icient to prevent oxidation of the magnesium and to control the desired quantitative recovery of resduum magnesium, thereafter raising the silicon content of the iron immediately preceding casting by inoculating the molten mass with a ferro-silicon alloy, casting the iron, which is white in the as-cast form, and

sequentially annealing same to yield nodular iron.

i References Cited in the ile of this patent UNITED STATES PATENTS Belgium Sept. 30, 1952 

1. IN THE MANUFACTURE OF CHILLED CAST AND ANNEALED NODULAR IRON HAVING SPHEROIDAL GRAPHITE, GRAPHITIC AGGREGATES AND FLAKES, THE PROCESS OF SIMULTANEOUSLY INJECTING MOLTEN METAL WITH CALCIUM CARBIDE AND A NODULIZING ALLOY CONTAINING MAGNESIUM, THE RELATIVE QUANTITY OF CALCIUM CARBIDE BEING SUFFICIENT TO PROTECT THE MAGNESIUM FROM OXIDATION AND TO CONTROL THE AMOUNT OF RESIDUAL MAGNESIUM WITHIN THE RANGE OF LESS THAN 0.01%, THEN COOLING AND SOLIDIFYING THE IRON AND THEREAFTER ANNEALING THE CASTING THEREOF. 